pid and execname mismatches

pid and execname mismatches

[tonyg362]

I'm trying to collect the pids and execnames of every process when it enters
the scheduler. The problem is that it seems as though the pid of the process
I use for the -c option always gives me the execname of the stapio process.
I thought maybe there was a problem with looking at the incorrect
task_struct because I am inside the scheduler, so I got this info directly
from the prev task_struct using context variables. e.g.

global pidlist

probe kernel.statement("schedule@kernel/sched.c:line#") {
    ppid = $prev->tgid
    name = kernel_string($prev->comm)

    if (!([ppid] in pidlist))
        pidlist[ppid] = name
}

probe end {
    foreach ([pid] in pidlist)
        printf("%d:%s\n", pid, pidlist[pid])
}

However, if I just hook into system calls and do a similar thing the pids
and execnames match up correctly. Am I doing something wrong?
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Re: pid and execname mismatches

[Mark Wielaard]

On Thu, 2010-07-22 at 07:29 -0700, tonyg362 wrote:
> I'm trying to collect the pids and execnames of every process when it enters
> the scheduler. The problem is that it seems as though the pid of the process
> I use for the -c option always gives me the execname of the stapio process.

This might come from the the following in runtime/staprun/mainloop.c:
#define WORKAROUND_BZ467568 1  /* PR 6964; XXX: autoconf when able */
I suspect that if you remove that line things work as expected. As the
comment says, it would be good to add some sort of autoconf for this.

Cheers,

Mark

Re: pid and execname mismatches

[Frank Ch. Eigler]

tonyg362 <tonyg3622@yahoo.com> writes:

> [...]
>     if (!([ppid] in pidlist))
>         pidlist[ppid] = name
> [...]

The problem here is that sometimes the execname() of a particular pid
changes, such as if it ever does an exec().  So you need to keep that
table updated even if a previous entry exists.

- FChE